Memory device with a fuse protection circuit

ABSTRACT

A memory device includes a memory circuit and a fuse protection circuit. The memory circuit includes a memory cell and a program line. The memory cell includes a fuse. The program line is configured to receive a program voltage for programming the fuse. The fuse protection circuit is coupled to the memory circuit and is configured to prevent unintentional programming of the fuse.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/433,279, filed Dec. 13, 2016, which is incorporated herein byreference in its entirety.

BACKGROUND

A memory device includes a memory cell operable so as to store a bit,i.e., ‘0’ or ‘1’, of data therein. The memory cell includes a fuse. Whenthe fuse is blown or programmed, a bit, e.g., ‘1’, is stored in thememory cell. Otherwise, i.e., when the fuse is left intact orunprogrammed, a bit, e.g., ‘0’, is stored.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a schematic diagram illustrating the first exemplary memorydevice in accordance with some embodiments.

FIG. 2 is a schematic diagram illustrating an exemplary memory circuit,an exemplary ESD protection circuit, and an exemplary fuse protectioncircuit in accordance with some embodiments.

FIG. 3 is a flow chart illustrating an exemplary method of operation ofa memory device in accordance with some embodiments.

FIG. 4 is a schematic diagram illustrating an exemplary program enablingcircuit in accordance with some embodiments.

FIG. 5 is a schematic diagram illustrating an exemplary detector inaccordance with some embodiments.

FIG. 6 is a schematic diagram illustrating the second exemplary memorydevice in accordance with some embodiments.

FIG. 7 is a flow chart illustrating an exemplary method of operation ofa memory device in accordance with some embodiments.

FIG. 8 is a schematic diagram illustrating the third exemplary memorydevice in accordance with some embodiments.

FIG. 9 is a flow chart illustrating an exemplary method of operation ofa memory device in accordance with some embodiments.

FIG. 10 is a schematic diagram illustrating an exemplary switch inaccordance with some embodiments.

FIG. 11 is a schematic diagram illustrating an exemplary switch inaccordance with some embodiments.

FIG. 12 is a schematic diagram illustrating the fourth exemplary memorydevice in accordance with some embodiments.

FIG. 13 is a flow chart illustrating an exemplary method of operation ofa memory device in accordance with some embodiments

FIG. 14 is a schematic diagram illustrating an exemplary detector and anexemplary switch in accordance with some embodiments.

FIG. 15 is a schematic diagram illustrating the fifth exemplary memorydevice in accordance with some embodiments.

FIG. 16 is a flow chart illustrating an exemplary method of operation ofa memory device in accordance with some embodiments

FIG. 17 is a schematic diagram illustrating an exemplary detector inaccordance with some embodiments

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

A read-only memory (ROM) device is a type of a non-volatile memory that,contrary to a volatile memory, does not require a supply voltage toretain data stored therein. FIG. 1 is a schematic diagram illustratingthe first exemplary memory device 100 in accordance with someembodiments. The example memory device 100 is a ROM device and includesa memory circuit 110, an electro-static discharge (ESD) protectioncircuit 120, and a fuse protection circuit 130.

The memory circuit 110 includes memory cells each configured to store abit, ‘0’ or ‘1’, of data therein using a fuse. For example, when a fuseof the memory cell is blown/programmed, a bit ‘1’ is stored in thememory cell. Otherwise, i.e., when the fuse is left intact/unprogrammed,a bit ‘0’ is stored. The fuse is susceptible to unintentionalprogramming. This risk is mitigated in certain embodiments herein. Inthe example of FIG. 1, the ESD protection circuit 120 is connected tothe memory circuit 110 through a line 140, e.g., a first program line(PL1) in FIG. 2, of the memory circuit 110 and is configured to protectcomponents of the memory circuit 110 from damages that may incur by anESD. In particular, when the line 140 is subjected to an ESD, the ESDprotection circuit 120 reduces an ESD voltage associated with the ESD toa reduced ESD voltage (Vesd). The reduced ESD voltage (Vesd) has anamount that is less an amount of the ESD voltage and that is tolerableby the components of the memory circuit 110. But, despite this ESDprotection circuit 120 mitigation, a reduced ESD current (Iesd)associated with the reduced ESD voltage (Vesd) may still flow through.Such a current (Iesd) may be sufficient to unintentionally program thefuse.

As will be described in detail below, the fuse protection circuit 130 isconfigured to prevent such an unintentional programming of the fuse. Inan exemplary embodiment, the fuse protection circuit 130 is connectedbetween the line 140 and another line 150, e.g., a second program line(PL2) in FIG. 2, of the memory circuit 110. When the aforementionedreduced ESD current (Iesd) flows through the line 140, the fuseprotection circuit 130 connects the line 150 to a ground, dischargingthe ESD current (Iesd) to the ground that may otherwise flow through andprogram the fuse.

FIG. 2 is a schematic diagram illustrating an exemplary memory circuit110, an exemplary ESD protection circuit 120, and an exemplary fuseprotection circuit 130 in accordance with some embodiments. The memorycircuit 110 includes a supply line (SL), a memory cell 210, a pass gatetransistor (M1), a word line driver 220, a word line (WL), a firstprogram line (PL1), a program enabling circuit 230, a bit line (BL), abit line selector 240, and a second program line (PL2).

The supply line (SL) is configured to receive a supply voltage, e.g.,VDD. The memory cell 210 includes an access transistor (M2) connected tothe ground and a fuse (F) connected between the pass gate transistor(M1) and the access transistor (M2). The word line driver 220 isconnected to the access transistor (M2) through the word line (WL). Thebit line selector 240 is connected to the pass gate transistor (M1)through the bit line (BL). The pass gate transistor (M1) is connected toan output terminal 230 c of the program enabling circuit 230 through thesecond program line (PL2). The program enabling circuit 230 has a firstinput terminal 230 a connected to the first program line (PL1) and asecond input terminal 230 b configured to receive an enable signal (EN).The program enabling circuit 230 is operable so as to allow and inhibitprogramming of the fuse (F) in response to the enable signal (EN). Forexample, when a level of the enable signal (EN) is high, the programenabling circuit 230 connects the second program line (PL2) to the firstprogram line (PL1) to thereby allow programming of the fuse (F).Otherwise, i.e., when the level of the enable signal (EN) is low, theprogram enabling circuit 230 disconnects the second program line (PL2)from the first program line (PL1), inhibiting programming of the fuse(F). In one embodiment, simultaneous with the inhibition of programmingthe fuse (F), the program enabling circuit 230 connects the secondprogram line (PL2) to the ground. As described below, this dischargesthe aforementioned reduced ESD current (Iesd).

The ESD protection circuit 120 includes clamping circuits 250, 260connected to the first program line (PL1) and the supply line (SL),respectively. The ESD protection circuit 120 is configured to detectpresence of an ESD event at the first program line (PL1) and the supplyline (SL) and to clamp/reduce an ESD voltage, e.g., about 2000V,associated with the ESD event to a reduced ESD voltage (Vesd), e.g., 2V.This causes a reduced ESD current (Iesd) associated with the reduced ESDvoltage (Vesd) to flow through the first program line (PL1). It is notedthat, without the fuse protection circuit 130, the reduced ESD current(Iesd) may further flow through and unintentionally program the fuse(F).

The fuse protection circuit 130 includes a detector 270 and switches(SW1, SW2, SW3). The detector 270 is configured to detect the reducedESD current (Iesd). The switches (SW1, SW2, SW3) are controlled by thedetector 270 to respectively connect the second program line (PL2), theword line (WL), and the supply line (SL) to the ground upon detection bythe detector 270 of the reduced ESD current (Iesd). In further detail,the detector 270 has an input terminal 270 a connected to the firstprogram line (PL1). The switch (SW1) has a first switch terminal (SW1 a)connected to an output terminal 270 b of the detector 270, a secondswitch terminal (SW1 b) connected to the second program line (PL2), anda third switch terminal (SW1 c) connected to the ground. The switch(SW2) has a first switch terminal (SW2 a) connected to the outputterminal 270 b of the detector 270, a second switch terminal (SW2 b)connected to the word line (WL), and a third switch terminal (SW2 c)connected to the ground. The switch (SW3) has a first switch terminal(SW3 a) connected to the output terminal 270 b of the detector 270, asecond switch terminal (SW3 b) connected to the supply line (SL), and athird switch terminal (SW3 c) connected to the ground. In someembodiments, one of the switches (SW1, SW2, SW3) is an n-typefield-effect transistor (FET). In other embodiments, one of the switches(SW1, SW2, SW3) is a p-type FET or any sort of transistor.

FIG. 3 is a flow chart illustrating an exemplary method 300 of operationof a memory device in accordance with some embodiments. The method 300will be described with further reference to FIG. 2 for ease ofunderstanding. It should be understood that the method 300 is applicableto structures other than that of FIG. 2. In operation 310, the programenabling circuit 230 is controlled to inhibit programming of the fuse(F). In this embodiment, operation 310 includes: a sub-operation 312 ofthe program enabling circuit 230 receiving an enable signal (EN), e.g.,at a low level; and a sub-operation 314 of the program enabling circuit230 disconnecting the second program line (PL2) from the first programline (PL1) in response to the enable signal (EN).

In operation 316, the fuse protection circuit 130 prevents unintentionalprogramming of the fuse (F). In this embodiment, operation 316 includes:a sub-operation 318 of the clamping circuit 250 detecting presence of anESD event at the first program line (PL1); a sub-operation 320 of theclamping circuit 250 clamping/reducing an ESD voltage associated withthe ESD event to a reduced ESD voltage (Vesd); a sub-operation 322 ofthe detector 270 detecting a reduced ESD current (Iesd) associated withthe reduced ESD voltage (Vesd); a sub-operation 324 of the detector 270generating a trigger signal (TRG) at a level, e.g., high, indicative ofthe reduced ESD current (Iesd) being detected by the detector 270; asub-operation 326 of the switches (SW1, SW2, SW3) receiving the triggersignal (TRG); and a sub-operation 328 of the switches (SW1, SW2, SW3)respectively connecting the second program line (PL2), the word line(WL), and the supply line (SL) to the ground in response to the triggersignal (TRG), discharging the reduced ESD current (Iesd).

In operation 330, the fuse (F) is programmed to store a bit, e.g., ‘1’,in the memory cell 210. In this embodiment, operation 330 includes: asub-operation 332 of the word line driver 220 driving, e.g., applying ahigh voltage level to, the word line (WL) to activate the accesstransistor (M2); a sub-operation 334 of the bit line selector 240selecting, e.g., applying a low voltage level to, the bit line (BL) toactivate the pass gate transistor (M1); a sub-operation 336 of theprogram enabling circuit 230 receiving an enable signal, e.g., at a highlevel; a sub-operation 338 of the program enabling circuit 230connecting the second program line (PL2) to the first program line (PL1)in response to the enable signal (EN); and a sub-operation 348 of thefirst program line (PL1) receiving a program voltage (Vprogram),resulting in a program current (Iprogram) that is associated with theprogram voltage (Vprogram) and that flows through, blowing/programming,the fuse (F).

FIG. 4 is a schematic diagram illustrating an exemplary program enablingcircuit 230 in accordance with some embodiments. The example programenabling circuit 230 includes first and second inverters 410, 420, eachof which includes a first inverter terminal 410 a, 420 a, a secondinverter terminal 410 b, 420 b, an input terminal 410 c, 420 c, and anoutput terminal 410 d, 420 d.

The first inverter terminals 410 a, 420 b serve as the first inputterminal 230 a of the program enabling circuit 230 and are thusconnected to the first program line (PL1). The second inverter terminals410 b, 420 b are connected to the ground. The input terminal 410 cserves as the second input terminal 230 b of the program enablingcircuit 230 and is thus configured to receive the enable signal (EN).The input terminal 420 c is connected to the output terminal 410 d. Theoutput terminal 420 d serves as the output terminal 230 c of the programenabling circuit 230 and is thus connected to the second program line(PL2).

In operation, when the enable signal (EN) is at a low level, e.g., whenit is desired to inhibit programming of the fuse (N), the first andsecond inverters 410, 420 disconnect the second program line (PL2) fromthe first program line (PL1) and connect the second program line (PL2)to the ground. On the other hand, when the enable signal is at a highlevel, e.g., when it is desired to program the fuse (N), the first andsecond inverters 410, 420 connect the second program line (PL2) to thefirst program line (PL1).

FIG. 5 is a schematic diagram illustrating an exemplary detector 270 inaccordance with some embodiments. The detector 270 includes a time delaycircuit 510 and first and second inverters 520, 530. In this embodiment,the time delay circuit 510 is in the form of an RC circuit and includesa resistor (R) and a capacitor (C). It should be understood that, afterreading this disclosure, the time delay circuit 510 can be in any formof time delay circuit, e.g., an RL or RLC circuit, so long as itachieves the intended purpose described herein. The resistor (R) isconnected between a node 510 c and the ground. The capacitor (C) has afirst capacitor terminal 510 a connected to the first program line (PL1)and a second capacitor terminal 510 b connected to the node 510 c. Thefirst inverter 520 has a first inverter terminal 520 a connected to thefirst program line (PL1), a second inverter terminal 520 b connected tothe ground, and an input terminal 520 c connected to the node 510 c. Thesecond inverter 520 has a first inverter terminal 520 a connected to thefirst program line (PL1), a second inverter terminal 530 b connected tothe ground, an input terminal 530 c connected to an output terminal 520d of the first inverter 520, and an output terminal 530 d that serves asthe output terminal 270 b of the detector 270 and that is thusconfigured to provide the trigger signal (TRG). The terminals 510 a, 520a, 530 a serve as the input terminal 270 a of the detector 270.

In operation, when the time delay circuit 510 receives a low-level nodesignal (N), the first and second inverters 520, 530 connect the outputterminal 530 d to the ground. As a result, a low-level trigger signal(TRG) is provided at the output terminal 530 d, indicating absence of anESD event. When the first program line (PL1) receives a program voltage(Vprogram), the time delay circuit 510 maintains the node signal (N) atthe low level. On the other hand, when an ESD event occurs at the firstprogram line (PL1), the time delay circuit 510 is unable to maintain thenode signal (N) at the low level. This causes the node signal (N) totransition to a high level. This, in turn, enables the first and secondinverters 520, 530 to connect the output terminal 530 d to the firstprogram line (PL1). As a result, the trigger signal (TRG) transitions toa high level.

FIG. 6 is a schematic diagram illustrating the second exemplary memorydevice 600 in accordance with some embodiments. This embodiment differsfrom the previous embodiment in that the fuse protection circuit 130 ofthe memory device 600 includes a detector 620 and switches (SW4, SW5,SW6). The detector 620 is configured to detect a reduced ESD current(Iesd) that flows through the supply line (SL). The switches (SW4, SW5,SW6) are controlled by the detector 620 to respectively connect thefirst program line (PL1), the second program line (PL2), and the wordline (WL) to the ground upon detection by the detector 620 of thereduced ESD current (Iesd). In further detail, the detector 620 has aninput terminal 620 a connected to the supply line (SL). The switch (SW4)has a first switch terminal (SW4 a) connected to an output terminal 620b of the detector 620, a second switch terminal (SW4 b) connected to thefirst program line (PL1), and a third switch terminal (SW4 c) connectedto the ground. The switch (SW5) has a first switch terminal (SW5 a)connected to the output terminal 620 b of the detector 620, a secondswitch terminal (SW5 b) connected to the second program line (PL2), anda third switch terminal (SW5 c) connected to the ground. The switch(SW6) has a first switch terminal (SW6 a) connected to the outputterminal 620 b of the detector 620, a second switch terminal (SW6 b)connected to the word line (WL), and a third switch terminal (SW6 c)connected to the ground.

FIG. 7 is a flow chart illustrating an exemplary method 700 of operationof a memory device in accordance with some embodiments. The method 700will be described with further reference to FIG. 6 for ease ofunderstanding. It should be understood that the method 700 is applicableto structures other than that of FIG. 6. In operation 710, the programenabling circuit 230 is controlled to inhibit programming of the fuse(F). In this embodiment, operation 710 includes: a sub-operation 712 ofthe program enabling circuit 230 receiving an enable signal (EN), e.g.,at a low level; and a sub-operation 714 of the program enabling circuit230 disconnecting the second program line (PL2) from the first programline (PL1) in response to the enable signal (EN).

In operation 716, the fuse protection circuit 130 prevents unintentionalprogramming of the fuse (F). In this embodiment, operation 716 includes:a sub-operation 718 of the clamping circuit 250 detecting presence of anESD event at the supply line (SL); a sub-operation 720 of the clampingcircuit 250 clamping/reducing an ESD voltage associated with the ESDevent to a reduced ESD voltage (Vesd); a sub-operation 722 of thedetector 620 detecting a reduced ESD current (Iesd) associated with thereduced ESD voltage (Vesd); a sub-operation 724 of the detector 620generating a trigger signal (TRG) at a level, e.g., high, indicative ofthe reduced ESD current (Iesd) being detected by the detector 620; asub-operation 726 of the switches (SW4, SW5, SW6) receiving the triggersignal (TRG); and a sub-operation 728 of the switches (SW4, SW5, SW6)respectively connecting the second program line (PL2), the first programline (PL1), and the word line (WL) to the ground in response to thetrigger signal (TRG), discharging the reduced ESD current (Iesd).

In operation 730, the fuse (F) is programmed to store a bit, e.g., ‘1’,in the memory cell 210. In this embodiment, operation 730 includes: asub-operation 732 of the word line driver 220 driving, e.g., applying ahigh voltage level to, the word line (WL) to activate the accesstransistor (M2); a sub-operation 734 of the bit line selector 240selecting, e.g., applying a low voltage level to, the bit line (BL) toactivate the pass gate transistor (M1); a sub-operation 736 of theprogram enabling circuit 230 receiving an enable signal (EN), e.g., at ahigh level; a sub-operation 738 of the program enabling circuit 230connecting the second program line (PL2) to the first program line (PL1)in response to the enable signal (EN); and a sub-operation 740 of thefirst program line (PL1) receiving a program voltage (Vprogram),resulting in a program current (Iprogram) that is associated with theprogram voltage (Vprogram) and that flows through, blowing/programming,the fuse (F).

FIG. 8 is a schematic diagram illustrating the third exemplary memorydevice 800 in accordance with some embodiments. This embodiment differsfrom the memory device 100 in that the fuse protection circuit 130 ofthe memory device 800 includes a detector 820 and a switch (SW7). Thedetector 820 is configured to detect the reduced ESD current (Iesd). Theswitch (SW7) is controlled by the detector 820 to operate the programenabling circuit 230 to connect the second program line (PL2) to theground upon detection by the detector 820 of the reduced ESD current(Iesd). The switch (SW7) is configured to operate the program enablingcircuit 230 to inhibit/allow programming of the fuse (F). In furtherdetail, the detector 820 has an input terminal 820 a connected to thefirst program line (PL1). The switch (SW7) has a first switch terminal(SW7 a) connected to an output terminal 820 b of the detector 820, asecond switch terminal (SW7 b) connected to the second input terminal230 b of the program enabling circuit 230, a third switch terminal (SW7c) connected to the ground, a fourth switch terminal (SW7 d) connectedto the first program line (PL1), and a fifth switch terminal (SW7 e)configured to receive a control signal (CTRL).

FIG. 9 is a flow chart illustrating an exemplary method 900 of operationof a memory device in accordance with some embodiments. The method 900will be described with further reference to FIG. 8 for ease ofunderstanding. It should be understood that the method 900 is applicableto structures other than that of FIG. 8. In operation 910, the programenabling circuit 230 is controlled to inhibit programming of the fuse(F). In this embodiment, operation 910 includes: a sub-operation 912 ofthe switch (SW7) receiving a control signal (CTRL), e.g., at a highlevel; a sub-operation 914 of the switch (SW7) generating an enablesignal (EN), e.g., at a low level, in response to the control signal(CTRL); a sub-operation 916 of the program enabling circuit 230receiving the enable signal (EN); and a sub-operation 918 of the programenabling circuit 230 disconnecting the second program line (PL2) fromthe first program line (PL1) in response to the enable signal (EN).

In operation 920, the fuse protection circuit 130 prevents unintentionalprogramming of the fuse (F). In this embodiment, operation 920 includes:a sub-operation 922 of the clamping circuit 250 detecting presence of anESD event at the first program line (PL1); a sub-operation 924 of theclamping circuit 250 clamping/reducing an ESD voltage associated withthe ESD event to a reduced ESD voltage (Vesd); a sub-operation 926 ofthe detector 820 detecting a reduced ESD current (Iesd) associated withthe reduced ESD voltage (Vesd); a sub-operation 928 of the detector 820generating a trigger signal (TRG) at a level, e.g., high, indicative ofthe reduced ESD current (Iesd) being detected by the detector 820; asub-operation 930 of the switch (SW7) receiving the trigger signal(TRG); a sub-operation 932 of the switch (SW7) generating an enablesignal (EN), e.g., at a low level, in response to the trigger signal(TRG); a sub-operation 934 of the program enabling circuit 230 receivingthe enable signal (EN); and a sub-operation 936 of the program enablingcircuit 230 connecting the second program line (PL2) to the ground inresponse to the enable signal (EN), discharging the reduced ESD current(Iesd).

In operation 938, the fuse (F) is programmed to store a bit, e.g., ‘1’,in the memory cell 210. In this embodiment, operation 938 includes: asub-operation 940 of the word line driver 220 driving, e.g., applying ahigh voltage level to, the word line (WL) to activate the accesstransistor (M2); a sub-operation 942 of the bit line selector 240selecting, e.g., applying a low voltage level to, the bit line (BL) toactivate the pass gate transistor (M1); a sub-operation 944 of theswitch (SW7) receiving a control signal (CTRL), e.g., at a low level; asub-operation 946 of the switch (SW7) generating an enable signal, e.g.,at a high level, in response to the control signal (CTRL); asub-operation 948 of the program enabling circuit 230 receiving theenable signal; a sub-operation 950 of the program enabling circuit 230connecting the second program line (PL2) to the first program line (PL1)in response to the enable signal (EN); and a sub-operation 952 of thefirst program line (PL1) receiving a program voltage (Vprogram),resulting in a program current (Iprogram) that is associated with theprogram voltage (Vprogram) and that flows through, blowing/programming,the fuse (F).

FIG. 10 is a schematic diagram illustrating an exemplary switch, e.g.,switch (SW7) of FIG. 8, in accordance with some embodiments. The switch(SW7) includes p-type FETs (M1, M2) and n-type FETs (M3, M4). The FET(M1) has a first source/drain terminal (M1 a) that serves as the fourthswitch terminal (SW7 d) of the switch (SW7) and that is thus connectedto the first program line (PL1). The FET (M2) has a first source/drainterminal (M2 a) connected to a second source/drain terminal (M1 b) ofthe FET (M1). Each of the FETs (M3, M4) has a first source/drainterminal (M3 a, M4 a) that is connected to a second source/drainterminal (M2 b) of the FET (M2) and a second source/drain terminal (M3b, M4 b) that serves as the third switch terminal (SW7 c) of the switch(SW7) and that is thus connected to the ground. The terminals (M2 b, M3a, M4 a) serve as second switch terminal (SW7 b) of the switch (SW7) andare thus connected to the second input terminal 230 b of the programenabling circuit 230 and configured to provide the enable signal (EN).Each of the FETs (M2, M4) further has a gate terminal (M2 c, M4 c) thatserves as the first switch terminal (SW7 a) of the switch (SW7) and thatis thus connected to the output terminal 820 b of the detector 820 andconfigured to receive the trigger signal (TRG). Each of the FETs (M1,M3) further has a gate terminal (M1 c, M3 c) that serves as the fifthswitch terminal (SW7 e) of the switch (SW7) and that is thus configuredto receive the control signal (CTRL).

In operation, when the control signal (CTRL) is at a high level, e.g.,when it is desired to inhibit programming of the fuse (N), the FET (M3)connects the terminals (M2 b, M3 a, M4 a) to the ground. As a result, alow-level enable signal (EN) is provided as an output. At this time,when the trigger signal (TRG) transitions to a high level, e.g., when anESD event occurs at the first program line (PL1), the FET (M4) connectsthe terminals (M2 b, M3 a, M4 a) to the ground. As a result, the enablesignal (EN) is maintained at the low level. On the other hand, when thecontrol signal (CTRL) is at a low level, e.g., when it is desired toprogram the fuse (N), and when the trigger signal is at a low level,e.g., in the absence of an ESD event, FETs (M1, M2) connect theterminals (M2 b, M3 a, M4 a) to the first program line (PL1). As aresult, a high-level enable signal (EN) is provided as an output.

FIG. 11 is a schematic diagram illustrating exemplary switch, e.g.,switch (SW7) of FIG. 6, in accordance with some embodiments. The switch(SW7) includes a p-type FET (M1), a resistor (R), and n-type FETs (M2,M3). The FET (M1) has a first source/drain terminal (M1 a) that servesthe fourth switch terminal (SW7 d) of the switch (SW7) and that is thusconnected to the first program line (PL1). The resistor (R) has a firstresistor terminal (Ra) connected to a second source/drain terminal (M1b) of the FET (M1). Each of the FETs (M2, M3) has a first source/drainterminal (M2 a, M3 a) that is connected to a second resistor terminal(Rb) of the resistor (R) and a second source/drain terminal (M2 b, M3 b)that serves as the third switch terminal (SW7 c) of the switch (SW7) andthat is thus connected to the ground. The terminals (Rb, M2 a, M3 a)serve as the second switch terminal (SW7 b) of the switch (SW7) and arethus connected to the second input terminal 230 b of the programenabling circuit 230 and configured to provide the enable signal (EN).The FET (M3) further has a gate terminal (M3 c) that serves as the firstswitch terminal (SW7 a) of the switch (SW7) and that is thus connectedto the output terminal 820 b of the detector 820 and configured toreceive the trigger signal (TRG). Each of the FETs (M1, M2) further hasa gate terminal (M1 c, M2 c) that serves as the fifth switch terminal(SW7 e) of the switch (SW7) and that is thus configured to receive thecontrol signal (CTRL).

In operation, when the control signal (CTRL) is at a high level, e.g.,when it is desired to inhibit programming of the fuse (N), the FET (M2)connects the terminals (Rb, M2 a, M3 a) to the ground. As a result, alow-level enable signal (EN) is provided as an output. At this time,when the trigger signal (TRG) transitions to a high level, e.g., when anESD event occurs at the first program line (PL1), the FET (M3) connectsthe terminals (Rb, M2 a, M3 a) to the ground. first program line (PL1).As a result, the enable signal (EN) is maintained at the low level. Onthe other hand, when the control signal (CTRL) is at a low level, e.g.,when it is desired to program the fuse (N), and when the trigger signalis at a low level, e.g., in the absence of an ESD event, FET (M1)connects the terminals (Rb, M2 a, M3 a) to the first program line (PL1).As a result, a high-level enable signal (EN) is provided as an output.

FIG. 12 is a schematic diagram illustrating the fourth exemplary memorydevice 1200 in accordance with some embodiments. This embodiment differsfrom the memory device 100 in that the fuse protection circuit 130 ofthe memory device 1200 includes a detector 1200 and a switch (SW8). Thedetector 1200 is configured to detect the reduced ESD current (Iesd).The switch (SW8) is controlled by the detector 1200 to operate theprogram enabling circuit 230 to connect the second program line (PL2) tothe ground upon detection by the detector 1200 of the reduced ESDcurrent (Iesd). The switch (SW7) is further controlled by the detector1200 to operate the program enabling circuit 230 to inhibit/allowprogramming of the fuse (F). In further detail, the detector 1200 has afirst input terminal 1220 a connected to the first program line (PL1)and a second input terminal 1220 b configured to receive a controlsignal (CTRL). The switch (SW8) has a first switch terminal (SW8 a)connected to an output terminal 1220 c of the detector 1220, a secondswitch terminal (SW8 b) connected to the second input terminal 230 b ofthe program enabling circuit 230, a third switch terminal (SW8 c)connected to the ground, and a fourth switch terminal (SW8 d) connectedto the first program line (PL1).

FIG. 13 is a flow chart illustrating an exemplary method 1300 ofoperation of a memory device in accordance with some embodiments. Themethod 1300 will be described with further reference to FIG. 12 for easeof understanding. It should be understood that the method 1300 isapplicable to structures other than that of FIG. 12. In operation 1310,the program enabling circuit 230 is controlled to inhibit programming ofthe fuse (F). In this embodiment, operation 1310 includes: asub-operation 1312 of the detector 1220 receiving a control signal(CTRL), e.g., at a high level; a sub-operation 1314 of the detector 1220generating a trigger signal (TRG), e.g., at a high level, in response tothe control signal (CTRL); a sub-operation 1316 of the switch (SW8)receiving the trigger signal (TRG); a sub-operation 1318 of the switch(SW8) generating an enable signal (EN), e.g., at a low level, inresponse to the trigger signal (TRG); a sub-operation 1330 of theprogram enabling circuit 230 receiving the enable signal (EN); and asub-operation 1322 of the program enabling circuit 230 disconnecting thesecond program line (PL2) from the first program line (PL1) in responseto the enable signal (EN).

In operation 1324, the fuse protection circuit 130 preventsunintentional programming of the fuse (F). In this embodiment, operation1324 includes: a sub-operation 1326 of the clamping circuit 250detecting presence of an ESD event at the first program line (PL1); asub-operation 1328 of the clamping circuit 250 clamping/reducing an ESDvoltage associated with the ESD event to a reduced ESD voltage (Vesd); asub-operation 1330 of the detector 1220 detecting the ESD current (Iesd)associated with the reduced ESD voltage (Vesd); a sub-operation 1332 ofthe detector 1220 generating a trigger signal (TRG) at a level, e.g.,high, indicative of the reduced ESD current (Iesd) being detected by thedetector 1220; a sub-operation 1334 of the switch (SW8) receiving thetrigger signal (TRG); a sub-operation 1336 of the switch (SW8)generating an enable signal (EN), e.g., at a high level, in response tothe trigger signal (TRG); a sub-operation 1338 of the program enablingcircuit 230 receiving the enable signal (EN); and a sub-operation 1340of the program enabling circuit 230 connecting the second program line(PL1) to the ground in response to the enable signal (EN), dischargingthe reduced ESD current (Iesd).

In operation 1342, the fuse (F) is programmed to store a bit, e.g., ‘1’,in the memory cell 210. In this embodiment, operation 1342 includes: asub-operation 1344 of the word line driver 220 driving, e.g., applying ahigh voltage level to, the word line (WL) to activate the accesstransistor (M2); a sub-operation 1346 of the bit line selector 240selecting, e.g., applying a low voltage level to, the bit line (BL) toactivate the pass gate transistor (M1); a sub-operation 1348 of thedetector 1220 receiving a control signal (CTRL), e.g., at a low level; asub-operation 1350 of the detector 1220 generating a trigger signal,e.g., at a low level, in response to the control signal (CTRL); asub-operation 1352 of the switch (SW8) receiving the trigger signal(TRG); a sub-operation 1354 of the switch (SW8) generating an enablesignal (EN), e.g., at a high level, in response to the trigger signal(TRG); a sub-operation 1356 of the program enabling circuit 230receiving the enable signal (EN); a sub-operation 1358 of the programenabling circuit 230 connecting the second program line (PL2) to thefirst program line (PL1) in response to the enable signal (EN); and asub-operation 1360 of the first program line (PL1) receiving a programvoltage (Vprogram), resulting in a program current (Iprogram) that isassociated with the program voltage (Vprogram) and that flows through,blowing/programming, the fuse (F).

FIG. 14 is a schematic diagram illustrating an exemplary detector, e.g.,detector 1220 of FIG. 12, and an exemplary switch, e.g., switch (SW8) ofFIG. 12, in accordance with some embodiments. The detector 1220 is inthe form of a time delay circuit and includes a capacitor (C) and aresistor (R). The capacitor (C) has a first capacitor terminal (Ca) thatserves as the first input terminal 1220 a of the detector 1220 and thatis thus connected to the first program line (PL1) and a second capacitorterminal (Cb) that is connected to a node 1410. The node 1410 serves asthe output terminal 1220 c of the detector 1220 and is thus configuredto provide the trigger signal (TRG). The resistor (R) has a firstresistor terminal (Ra) that is connected to the node 1410 and a secondresistor terminal (Rb) that serves as the second input terminal 1220 bof the detector 1220 and that is thus configured to receive the controlsignal (CTRL).

The switch (SW8) is in the form of an inverter and has a first inverterterminal 1420 that serves as the fourth switch terminal (SW8 d) of theswitch (SW8) and that is thus connected to the first program line (PL1),a second inverter terminal 1430 that serves as the third switch terminal(SW8 c) of the switch (SW8) and that is thus connected to the ground, aninput terminal 1440 that serves as the first switch terminal (SW8 a) ofthe switch (SW8) and that is thus configured to receive the triggersignal (TRG), and an output terminal 1450 that serves as the secondswitch terminal (SW8 b) of the switch (SW8) and that is thus configuredto provide the enable signal (EN).

In operation, when the time delay circuit 1420 receives a high-levelcontrol signal (CTRL), e.g., when it is desired to inhibit programmingof the fuse (N), the inverter (SW8) receives a high-level trigger signal(TRG) and connects the output terminal 1450 to the ground. As a result,a low-level enable signal (EN) is provided at the output terminal 1450.At this time, when an ESD event occurs at the first program line (PL1),the time delay circuit 1420 maintains the trigger signal (TRG) at thehigh level. On the other hand, when the time delay circuit 1420 receivesa low-level control signal (CTRL), e.g., when it is desired to programthe fuse (N), the inverter (SW8) receives a low-level trigger signal(TRG) and connects the output terminal 1450 to the first program line(PL1). As a result, a high-level enable signal (EN) is provided at theoutput terminal 1450. At this time, when a program voltage (Vprogram) isapplied to the first program line (PL1), the time delay circuit 1420maintains the trigger signal (TRG) at the low level.

FIG. 15 is a schematic diagram illustrating the fifth exemplary memorydevice 1500 in accordance with some embodiments. This embodiment differsfrom the memory device 100 in that fuse protection circuit 130 of thememory device 1500 includes a detector 1520 and switches (SW9, SW10).The detector 1520 has a first input terminal 1520 a connected to thefirst program line (PL1) and a second input terminal 1529 b connected tothe supply line (SL). The switch (SW9) has a first switch terminal (SW9a) connected to an output terminal 1520 c of the detector 1520, a secondswitch terminal (SW9 b) connected to the second program line (PL2), anda third switch terminal (SW9 c) connected to the ground. The switch(SW10) has a first switch terminal (SW10 a) connected to the outputterminal 1520 c of the detector 1520, a second switch terminal (SW10 b)connected to the word line (WL), and a third switch terminal (SW10 c)connected to the ground. In some embodiments, one of the switches (SW9,SW10) is an n-type FET. In other embodiments, one of the switches (SW9,SW10) is a p-type FET or any sort of transistor.

FIG. 16 is a flow chart illustrating an exemplary method 1600 ofoperation of a memory device in accordance with some embodiments. Themethod 300 will be described with further reference to FIG. 15 for easeof understanding. It should be understood that the method 1600 isapplicable to structures other than that of FIG. 15. In operation 1610,the program enabling circuit 230 is controlled to inhibit programming ofthe fuse (F). In this embodiment, operation 1610 includes: asub-operation 1612 of the program enabling circuit 230 receiving anenable signal (EN), e.g., at a low level; and a sub-operation 1614 ofthe program enabling circuit 230 disconnecting the second program line(PL2) from the first program line (PL1) in response to the enable signal(EN).

In operation 1616, the fuse protection circuit 130 preventsunintentional programming of the fuse (F). In this embodiment, operation1616 includes: a sub-operation 1618 of the ESD protection circuit 120detecting presence of an ESD event at the first program line (PL1) andthe supply line (SL); a sub-operation 1620 of the ESD protection circuit120 clamping/reducing an ESD voltage associated with the ESD event andat the first program line (PL1) and/or the supply line (SL) to a reducedESD voltage (Vesd); a sub-operation 1622 of the detector 1520 detectinga reduced ESD current (Iesd) associated with the reduced ESD voltage(Vesd); a sub-operation 1624 of the detector 1520 generating a triggersignal (TRG) at a level, e.g., high, indicative of the reduced ESDcurrent (Iesd) being detected by the detector 1520; a sub-operation 1626of the switches (SW9, SW10) receiving the trigger signal (TRG); and asub-operation 1628 of the switches (SW9, SW10) respectively connectingthe second program line (PL2) and the word line (WL) to the ground inresponse to the trigger signal (TRG), discharging the ESD current(Iesd).

In operation 1630, the fuse (F) is programmed to store a bit, e.g., ‘1’,in the memory cell 210. In this embodiment, operation 1630 includes: asub-operation 1632 of the word line driver 220 driving, e.g., applying ahigh voltage level to, the word line (WL) to activate the accesstransistor (M2); a sub-operation 1634 of the bit line selector 240selecting, e.g., applying a low voltage level to, the bit line (BL) toactivate the pass gate transistor (M1); a sub-operation 1636 of theprogram enabling circuit 230 receiving an enable signal, e.g., at a highlevel; a sub-operation 1638 of the program enabling circuit 230connecting the second program line (PL2) to the first program line (PL1)in response to the enable signal (EN); and a sub-operation 1640 of thefirst program line (PL1) receiving a program voltage (Vprogram),resulting in a program current (Iprogram) that is associated with theprogram voltage (Vprogram) and that flows through, blowing/programming,the fuse (F).

FIG. 17 is a schematic diagram illustrating an exemplary detector 1520in accordance with some embodiments. The detector 1520 is in the form ofa time delay circuit and includes capacitors (C1, C2), p-type FETs (M1,M2), and a resistor (R). The resistor (R) is connected between a node1710 and the ground. The node 1710 serves as the output terminal 1120 cof the detector 1120 and is thus configured to provide the triggersignal (TRG). Each of the FETs (M1, M2) has a first source/drainterminal (M1 a, M2 a) connected to the node 1710 and a gate terminal (M1c, M2 c) connected to a respective one of the first program line (PL1)and the supply line (SL). Each of the capacitors (C1, C2) has a firstcapacitor terminal (C1 a, C2 a) connected to a second source/drainterminal (M1 b, M2 b) of a respective one of the FETs (M1, M2) and asecond capacitor terminal (C1 b, C2 b) connected to a respective one ofthe supply line (SL) and the first program line (PL1). The terminals (M1c, C2 b) serve as the first input terminal 1520 a of the detector 1520.The terminals (M2 c, C1 b) serve as the second input terminal 1520 b ofthe detector 1520.

In operation, the FET (M2) first connects the capacitor (C2) to theresistor (R). As a result, a low-level trigger signal (TRG) appears atthe node 1720. Then, when the first program line (PL1) receives aprogram voltage (Vprogram), the time delay circuit 1520 maintains thetrigger signal (TRG) at the low level. On the other hand, when an ESDevent occurs at the first program line (PL1), the time delay circuit1520 is unable to maintain the trigger signal (TRG) at the low level. Asa result, the trigger signal (TRG) transitions to a high level.

Similarly, the FET (M1) first connects the capacitor (C1) to theresistor (R). As a result, a low-level trigger signal (TRG) appears atthe node 1710. Then, when the supply line (SL) receives a supply voltage(VDD), the time delay circuit 1520 maintains the trigger signal (TRG) atthe low level. On the other hand, when an ESD event occurs at the supplyline (SL), the time delay circuit 1520 is unable to maintain the triggersignal (TRG) at the low level. As a result, the trigger signal (TRG)transitions to a high level.

In one embodiment, a memory device comprises a memory circuit and a fuseprotection circuit. The memory circuit includes a supply line, a programline, and a memory cell. The supply line is configured to receive asupply voltage. The memory cell includes a fuse. The program line isconfigured to receive a program voltage for programming the fuse. Thefuse protection circuit is coupled to the memory circuit, is configuredto prevent unintentional programming of the fuse, and includes adetector and a switch. The detector is configured to detect anelectro-static discharge (ESD) current that flows through one of thesupply line and the program line. The switch is configured to couple theother of the supply line and the program line to a ground when thedetector detects the ESD current.

In another embodiment, a memory device comprises a memory circuit and afuse protection circuit. The memory circuit includes a supply line, amemory cell, and a word line. The supply line is configured to receive asupply voltage. The memory cell includes a fuse. The program line isconfigured to receive a program voltage for programming the fuse. Theword line is coupled to the memory cell. The fuse protection circuit iscoupled to the memory circuit, is configured to prevent unintentionalprogramming of the fuse, and includes a detector and a switch. Thedetector is configured to detect an electro-static discharge (ESD)current that flows through one of the supply line and the program line.The switch is configured to couple the word line to a ground when thedetector detects the ESD current.

In another embodiment, a method for preventing unintentional programmingof a fuse of a memory cell of a memory device is provided. The memorydevice includes a first program line and a second program line coupledto the memory cell and selectively coupled to the first program line.The method comprises: detecting an electro-static discharge (ESD)current flowing through one of the first program line and a supply line;and generating a trigger signal based on detection of the ESD currentthat causes decoupling of the second program line from the first programline and coupling of the second program line to a ground, therebydischarging the ESD current.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A memory device comprising: a memory circuitincluding a supply line configured to receive a supply voltage, a memorycell including a fuse, and a program line configured to receive aprogram voltage for programming the fuse; and a fuse protection circuitcoupled to the memory circuit and configured to prevent unintentionalprogramming of the fuse, the fuse protection circuit including adetector configured to generate a trigger signal in response to anelectro-static discharge (ESD) current that flows through one of thesupply line and the program line, and a switch configured to couple theother of the supply line and the program line to a ground when thetrigger signal indicates presence of the ESD current on one of thesupply line and the program line.
 2. The memory device of claim 1,further comprising an ESD protection circuit coupled to the memorycircuit and configured to reduce an ESD voltage to a reduced ESDvoltage, wherein the ESD current is associated with the reduced ESDvoltage.
 3. The memory device of claim 1, further comprising: a secondprogram line selectively coupled to the program line; and a secondswitch coupled to the detector and the second program line andconfigured to couple the second program line to the ground when thetrigger signal indicates presence of the ESD current on one of thesupply line and the program line.
 4. The memory device of claim 1,further comprising: a word line coupled to the memory cell; and a secondswitch coupled to the detector and the word line and configured tocouple the word line to the ground when the detector detects the ESDcurrent.
 5. The memory device of claim 1, further comprising: a secondprogram line; and a program enabling circuit coupled between the programline and the second program line and configured to receive an enablesignal and to selectively couple and decouple the second program line toand from the program line in response to the enable signal.
 6. Thememory device of claim 5, wherein the program enabling circuit isfurther configured to selectively couple and decouple the second programline to and from the ground in response to the enable signal.
 7. Amemory device comprising: a memory circuit including a supply lineconfigured to receive a supply voltage, a memory cell including a fuse,and a program line configured to receive a program voltage forprogramming the fuse, and a word line coupled to the memory cell; and afuse protection circuit coupled to the memory circuit and configured toprevent unintentional programming of the fuse, the fuse protectioncircuit including a detector configured to generate a trigger signal inresponse an electro-static discharge (ESD) current that flows throughone of the supply line and the program line, and a switch configured tocouple the word line to a ground when the detector detects the ESDcurrent.
 8. The memory device of claim 7, further comprising: a secondprogram line selectively coupled to the program line; and a secondswitch coupled to the detector and the second program line andconfigured to couple the second program line to the ground when thetrigger signal indicates presence of the ESD current on one of thesupply line and the program line.
 9. The memory device of claim 7,further comprising a second switch coupled to the detector and theprogram line and configured to couple the program line to the groundwhen the trigger signal indicates presence of the ESD current on one ofthe supply line and the program line.
 10. The memory device of claim 7,further comprising a second switch coupled to the detector and thesupply line and configured to couple the supply line to the ground whenthe trigger signal indicates presence of the ESD current on one of thesupply line and the program line rent.
 11. The memory device of claim 7,further comprising: a second program line; and a program enablingcircuit coupled between the program line and the second program line andconfigured to receive an enable signal and to selectively couple anddecouple the second program line to and from the program line inresponse to the enable signal.
 12. The memory device of claim 11,wherein the program enabling circuit is further configured toselectively couple and decouple the second program line to and from theground in response to the enable signal.
 13. A method for preventingunintentional programming of a fuse of a memory cell of a memory device,the memory device including a first program line and a second programline coupled to the memory cell and selectively coupled to the firstprogram line, the method comprising: generating a trigger signal inresponse to an electro-static discharge (ESD) current flowing throughone of the first program line and a supply line; and in response to thetrigger signal, decoupling the second program line from the firstprogram line and coupling of the second program line to a ground,thereby discharging the ESD current.
 14. The method of claim 13, furthercomprising: detecting presence of an ESD event at one of the firstprogram line and the supply line; and reducing an ESD voltage associatedwith the ESD event to a reduced ESD voltage, the ESD current beingassociated with the reduced ESD voltage.
 15. The method of claim 13,further comprising, in response to the trigger signal, coupling thesecond program line to the ground.
 16. The method of claim 13, furthercomprising: in response to the trigger signal, generating an enablesignal; and in response to the enable signal, coupling the secondprogram line to the ground.
 17. The method of claim 13, furthercomprising, in response to the trigger signal, coupling a word linecoupled to the memory cell to the ground.
 18. The method of claim 13,further comprising, in response to the trigger signal, coupling thefirst program line to the ground.
 19. The method of claim 13, furthercomprising, in response to the trigger signal, coupling the supply lineto the ground.
 20. The method of claim 13, further comprising: receivinga control signal; and in response to the control signal, generating thetrigger signal for causing coupling of the second program line to thefirst program line.